1. Field of the Invention
The present invention relates to a thermoplastically re-formable plastic sheet or plate with flameproofing means, useful for interior structures in passenger vehicles, passenger ships, and passenger aircraft, and for producing structural elements suitable for installation in such conveyances.
2. Discussion of the Background
Experience has shown that the time required to evacuate large capacity conveyances, such as airplanes, in the case of fire is so lengthy that the health and life of the passengers are at hazard. Therefore, materials are used in interior structures of such conveyances which do not present additional hazards for the passengers. Such materials should exhibit a minimal emission of heat, smoke, and toxic gases during fires, and the onset of any such emissions should be delayed as long as possible.
In the past a number of thermoplastic plastic materials such as ABS, PC, or PES have been used for interior structures of aircraft. These materials release substantial heat immediately after ignition. Moreover, ABS emits substantial smoke. Therefore these plastics are no longer acceptable for interior structures of aircraft.
The U.S. Federal Aviation Authority, in coordination with the aircraft manufacturers, has established, e.g., the following requirements relating to measurement methods and limiting values of parameters, for the testing of the suitability of materials for interior structures of aircraft:
TABLE ______________________________________ Prescribed Parameter Measured value Units maximum ______________________________________ Heat evolution HRR kW/m.sup.2 65 FAR 25,853 (OSU) HR kW-min/m.sup.2 65 Density of evolved D.sub.s (4 min) 100 smoke Toxic gases CO ppm 3,500 S0.sub.2, H.sub.2 S ppm 100 ______________________________________
Thermoplastics modified with flame-protective additives according to DE-A 38 29 712 (corresponds to U.S. Pat. No. 4,981,895, incorporated herein by reference) meet these fire regulations. The additives improve the combustion properties in the OSU chamber test. In comparison to ABS, PC, and PES, plastics modified with the additives substantially improve the fire safety of passengers when said plastics are used in the inner structures of passenger conveyances. Accordingly, such modified plastics are used in large amounts in the aircraft industry.
Nonetheless, these modified plastics have certain disadvantages. The impact strength (Gardner) of sheets comprised of the modified plastics decreases with increasing content of the flame-retardant additives. In addition, the HRR values determined in the OSU test still appear to be close to the maximum permissible values, particularly in the case of 2-5 mm thick sheets, which are particularly important in interior construction. Furthermore, some of the additives used, particularly boron trioxide, form undesirable deposits or efflorescences or blooms on the surface of the sheets.